The impact of a 4^th generation on mixing and CP violation in the charm system

We study D⁰-D⁰ mixing in the presence of a fourth generation of quarks. In particular, we calculate the size of the allowed CP violation which is found at the observable level well beyond anything possible with CKM dynamics. We calculate the semileptonic asymmetry a_SL(D) and the mixing induced CP asymmetry η_f S_f (D) which are correlated with each other. We also investigate the correlation of η_f S_f (D) with a number of prominent observables in other mesonic systems like ε^′/ε, Br(K_L → π⁰νν), Br(K⁺ → π⁺νν), Br(B_s → µ⁺µ⁻), Br(B_d → µ⁺µ⁻) and finally S_ψφ(B_s) in the B_s system. We identify a clear pattern of flavour and CP violation predicted by the SM4 model: While simultaneous large 4G effects in the K and D systems are possible, accompanying large NP effects in the B_d system are disfavoured. However this behaviour is not as pronounced as found for the LHT and RSc models. In contrast to this, sizeable CP violating effects in the B_s system are possible unless extreme effects in η_f S_f (D) are found, and Br(B_s → µ⁺µ⁻) can be strongly enhanced regardless of the situation in the D system. We find that, on the other hand, S_ψφ(B_s) > 0.2 combined with the measured ε^′/ε significantly diminishes 4G effects within the D system.